Assessing the impact of shading by solar panels on evapotranspiration and plant growth using lysimeters

Photovoltaics is one of the front-running renewable energy technologies, greatly contributing to the reduction in greenhouse gas emissions. With the aim for carbon neutrality ever larger photovoltaics plants are being built worldwide alongside an increasing number of small-scale Agri-Voltaics (APV) systems. Despite this trend, the impact of such systems on the environment remains scarcely studied. By means of lysimeters the effect of shading by solar panels on evapotranspiration (ET) and plant growth has been analyzed at a research station in Germany. During the measurement period which stretched from November 2019 to early April 2020, ET recorded at the area shaded by the panels was with 163 mm almost equal to ET at the reference site with 158 mm. However, percolation was found to be much higher at the reference site with 89.5 mm compared to the area below the panel where no seepage was detected. This difference was investigated by looking more in depth at the temporal evolution of ET, which showed to be season-dependent with lower ET below the panel than at the reference site during the growing season but higher ET below the panel the rest of the year. During the growing season, shading leads to a strong reduction of solar radiation received by the area below the panel resulting in lower soil temperatures and lower evapotranspiration than at the unshaded reference area. During the winter months in turn the panels raise soil temperatures by trapping outgoing radiation which results in higher evapotranspiration below the panels than at the reference area. The described effects of the panels on solar radiation and temperature have been studied at a conventional photovoltaics park and are described alongside the measurements from the lysimeter station within this paper. While at the end of the period of shading the height of rape was found to be on average 20 cm higher below the panel than at the reference site, rape yield in turn was lower assumingly due to a lack of light in the early stages of plant development. This paper presents the measurement results from the lysimeter station and discusses the underlying processes of changes in temperature and global radiation in respect to the soil-water-plant system.